Obama Girds for Battle With Congress on Iran Deal

President delivers forceful defense of nuclear agreement a day after it was reached.

President Barack Obama delivered an unusually animated and sometimes combative defense of the Iran nuclear deal the day after it was reached, girding for a complicated political challenge likely to force him to use his veto to save his crowning foreign-policy achievement.

Lawmakers have 60 days to review the agreement and an option to vote on approving or disapproving it, with opposition to the deal widespread among Republicans who control both houses of Congress. If they vote it down, the deal’s survival will hinge on Mr. Obama’s ability to secure enough support from his own Democratic Party to prevent a two-thirds majority in each chamber from overriding his promised veto.

Opponents of the deal ramped up their criticism and organization against it on Wednesday.

Mr. Obama, in a 67-minute news conference at the White House, accused opponents—from Israeli leader Benjamin Netanyahu to Republican lawmakers—of pushing political talking points to simply discredit the accord as a bad deal.

“Either the issue of Iran obtaining a nuclear weapon is resolved diplomatically through a negotiation or it’s resolved through force, through war,” he added. “Those are the options.”

The president’s aggressive defense of the deal drew quick pushback from Republicans in Congress, where the criticism has largely been twofold: that the agreement won’t stop Iran from acquiring a nuclear weapon and that it doesn’t address broader concerns about Tehran’s behavior in the region. Rep. Lee Zeldin (R., N.Y.) disputed the president’s assertion that this is a choice between the accord or war.

“Here’s an alternative other than war: A better deal,” Mr. Zeldin said. “For the security of America and the stability of the Middle East, we must pursue a better direction immediately.”